FTP blogs are not publishing their site feeds in RSS format. Until this is fixed, either use the atom.xml feed instead (most feed readers that accept RSS accept Atom as well) or use: http://www.blogger.com/feeds/
blogid/posts/default?alt=rss to get your blog’s feed in RSS format.
Update, 11/21: This has been fixed. FTP blogs now publish an rss.xml file.